This invention relates to a `green` (environmentally friendly) power supply for a small calculator, e.g., a pocket calculator, a hand-held calculator or a desk-top calculator.
Small calculators, e.g., pocket calculators, hand-held calculators and desk-top calculators, require appropriate power supplies so as to support normal functions thereof. Such power supplies are classified into two types: batteries and solar cells. Such batteries are classified into three sorts: nickel-chromium batteries, nickel-cadmium batteries and mercury batteries. Such batteries must be disposed of after use, and unfortunately cause serious environmental problems. There have been `green` batteries, but such batteries have not been successfully commercialized due to their high costs. Solar cells do not cause serious environmental problems, as they last a long time. However, as solar cells are dependent on sufficient light, they can be used only in certain places wherein light is sufficient. Therefore, there is a unfulfilled need for a `green` power supply which functions normally regardless of light intensity and is inexpensive.